I think UA might add this sooner if it proves to be revenue generating for the other airlines. If it's just a nice to have option that does not pay for itself then I don't think we will see it soon. On the other hand if they price it right I think it could be a real money maker.
IPass (www.ipass.com) which many corporations give to corporate travelers to use for WIFI and dialup internet access around the world has just added the Boeing Conexion as a roaming partner so if you have nice base of corporate customers who can easily bill the cost to their employer it might take off!

I wonder what the cost is to outfit an aircraft and what the projected ROI would be?